Pt sorption on Mn(IV) oxide
Description
We investigated the sorption mechanism to clarify the processes responsible for Pt enrichment in marine Fe-Mn nodules and crusts. For this aim, we conducted sorption experiments to determine the distribution coefficients of Pt(II) onto δ-MnO2 in NaCl solutions, followed by XAFS measurements of Pt-sorbed δ-MnO2. The sorption of Pt(II) depended on the Cl− concentration and pH, reflecting Pt speciation in the solution. XAFS analysis demonstrated that negatively charged chloro-complexes, such as PtCl42− in a NaCl solution, were adsorbed on δ-MnO2 through ligand exchange. Subsequently, Pt(II) was oxidized into Pt(IV) on δ-MnO2, transforming the square planar coordination into octahedral coordination. The octahedral coordination of Pt(IV) formed a triple-corner sharing complex above vacancy sites. Finally, Pt(IV) was incorporated into MnO6 octahedral sheets through isomorphous substitution of Pt(IV) for Mn(IV) sites.
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Pt concentrations were meausred using ICP-MS. XAFS spectra were collected in beamline BL-12C at Photon Factory, KEK (Tsukuba, Japan).